Patent Documents 1 and 2 disclose a related art buckle structure. For example, the buckle structure disclosed in Patent Document 1 includes a seat belt that may restrain an occupant, a tongue member that is provided at the end of the seat belt, and a buckle member that may lock the tongue member.
Further, in the above-mentioned technique, a buckle member is disposed so as to be received in a recess of a seat cushion (a receiving portion formed below the lumbar portion of an occupant). In this way, it may be possible to prevent or suppress the separation of the buckle member from the seat cushion while improving the seat performance of a seat. Furthermore, in the above-mentioned technique, it may be possible to improve an occupant restraining force of the seat belt by disposing the buckle member in the receiving portion (below the lumbar portion of the occupant).
However, in the technique disclosed in Patent Document 1, it might be difficult to find the buckle member, which is received in the receiving portion, at first glance. Therefore, it takes an occupant a long time to lock the tongue member to the buckle member, which causes convenience to slightly deteriorate.
Meanwhile, Patent Document 2 discloses a technique for providing a buckle member at the side portion of the seat cushion through a link mechanism. The link mechanism includes first and second link arms (which are long plate-shaped members).
Further, in this technique, an upper end (rotating shaft) of the first link arm is rotatably supported by the side portion of the seat cushion. When the first link arm is rotated around the rotating shaft, a lower end of the first link arm ascends toward the front side of the seat from a position facing the lower side of a seat.
Furthermore, the second link arm is held on the side portion of the seat cushion while being inclined upward toward the front side of the seat. Moreover, a lower end of the second link arm is rotatably supported by a lower end of the first link arm, and the buckle member is attached at an upper end of the second link arm.
Further, in the technique disclosed in Patent Document 2, the upper end of the second link arm ascends toward the front side of the seat when the first link arm is rotated around the rotating shaft. Accordingly, the buckle member may be disposed so as to protrude from the surface of the seat cushion (the buckle member may be disposed so as to be conspicuous).
Furthermore, an occupant locks the tongue member to the buckle member after fastening the seat belt. Moreover, when the first link arm is rotated around the rotating shaft in a reverse direction, the upper end of the second link arm descends toward the rear side of the seat. Accordingly, it may be possible to maintain an occupant restraining force of the seat belt by disposing the buckle member below the surface of the seat cushion (below the lumbar portion of the occupant).